Rollup merge of #44775 - MaloJaffre:debug-struct, r=sfackler

Refactor to use `debug_struct` in several Debug impls

Also use `pad` and derive `Debug` for `Edge`.

Fixes #44771.

7 files changed, 42 insertions, 61 deletions

diff --git a/src/librustc_data_structures/graph/mod.rs b/src/librustc_data_structures/graph/mod.rs
index 474622f3669..56d5f5ffa3f 100644
--- a/src/librustc_data_structures/graph/mod.rs
+++ b/src/librustc_data_structures/graph/mod.rs
@@ -31,7 +31,7 @@
 //! be indexed by the direction (see the type `Direction`).
 
 use bitvec::BitVector;
-use std::fmt::{Formatter, Error, Debug};
+use std::fmt::Debug;
 use std::usize;
 use snapshot_vec::{SnapshotVec, SnapshotVecDelegate};
 
@@ -48,6 +48,7 @@ pub struct Node<N> {
     pub data: N,
 }
 
+#[derive(Debug)]
 pub struct Edge<E> {
     next_edge: [EdgeIndex; 2], // see module comment
     source: NodeIndex,
@@ -69,18 +70,6 @@ impl<N> SnapshotVecDelegate for Edge<N> {
     fn reverse(_: &mut Vec<Edge<N>>, _: ()) {}
 }
 
-impl<E: Debug> Debug for Edge<E> {
-    fn fmt(&self, f: &mut Formatter) -> Result<(), Error> {
-        write!(f,
-               "Edge {{ next_edge: [{:?}, {:?}], source: {:?}, target: {:?}, data: {:?} }}",
-               self.next_edge[0],
-               self.next_edge[1],
-               self.source,
-               self.target,
-               self.data)
-    }
-}
-
 #[derive(Copy, Clone, PartialEq, Eq, Debug, Hash)]
 pub struct NodeIndex(pub usize);
 
diff --git a/src/libstd/sync/mpsc/mod.rs b/src/libstd/sync/mpsc/mod.rs
index dcd4c8dfdf5..ce1a07b31b2 100644
--- a/src/libstd/sync/mpsc/mod.rs
+++ b/src/libstd/sync/mpsc/mod.rs
@@ -919,7 +919,7 @@ impl<T> Drop for Sender<T> {
 #[stable(feature = "mpsc_debug", since = "1.8.0")]
 impl<T> fmt::Debug for Sender<T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "Sender {{ .. }}")
+        f.debug_struct("Sender").finish()
     }
 }
 
@@ -1049,7 +1049,7 @@ impl<T> Drop for SyncSender<T> {
 #[stable(feature = "mpsc_debug", since = "1.8.0")]
 impl<T> fmt::Debug for SyncSender<T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "SyncSender {{ .. }}")
+        f.debug_struct("SyncSender").finish()
     }
 }
 
@@ -1551,7 +1551,7 @@ impl<T> Drop for Receiver<T> {
 #[stable(feature = "mpsc_debug", since = "1.8.0")]
 impl<T> fmt::Debug for Receiver<T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "Receiver {{ .. }}")
+        f.debug_struct("Receiver").finish()
     }
 }
 
@@ -3009,22 +3009,4 @@ mod sync_tests {
             repro()
         }
     }
-
-    #[test]
-    fn fmt_debug_sender() {
-        let (tx, _) = channel::<i32>();
-        assert_eq!(format!("{:?}", tx), "Sender { .. }");
-    }
-
-    #[test]
-    fn fmt_debug_recv() {
-        let (_, rx) = channel::<i32>();
-        assert_eq!(format!("{:?}", rx), "Receiver { .. }");
-    }
-
-    #[test]
-    fn fmt_debug_sync_sender() {
-        let (tx, _) = sync_channel::<i32>(1);
-        assert_eq!(format!("{:?}", tx), "SyncSender { .. }");
-    }
 }
diff --git a/src/libstd/sync/mpsc/select.rs b/src/libstd/sync/mpsc/select.rs
index e49f4cff024..a9f3cea243f 100644
--- a/src/libstd/sync/mpsc/select.rs
+++ b/src/libstd/sync/mpsc/select.rs
@@ -354,13 +354,13 @@ impl Iterator for Packets {
 
 impl fmt::Debug for Select {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "Select {{ .. }}")
+        f.debug_struct("Select").finish()
     }
 }
 
 impl<'rx, T:Send+'rx> fmt::Debug for Handle<'rx, T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "Handle {{ .. }}")
+        f.debug_struct("Handle").finish()
     }
 }
 
@@ -774,18 +774,4 @@ mod tests {
             }
         }
     }
-
-    #[test]
-    fn fmt_debug_select() {
-        let sel = Select::new();
-        assert_eq!(format!("{:?}", sel), "Select { .. }");
-    }
-
-    #[test]
-    fn fmt_debug_handle() {
-        let (_, rx) = channel::<i32>();
-        let sel = Select::new();
-        let handle = sel.handle(&rx);
-        assert_eq!(format!("{:?}", handle), "Handle { .. }");
-    }
 }
diff --git a/src/libstd/sync/mutex.rs b/src/libstd/sync/mutex.rs
index 1d62853e906..eb507858b92 100644
--- a/src/libstd/sync/mutex.rs
+++ b/src/libstd/sync/mutex.rs
@@ -394,11 +394,18 @@ impl<T: ?Sized + Default> Default for Mutex<T> {
 impl<T: ?Sized + fmt::Debug> fmt::Debug for Mutex<T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self.try_lock() {
-            Ok(guard) => write!(f, "Mutex {{ data: {:?} }}", &*guard),
+            Ok(guard) => f.debug_struct("Mutex").field("data", &&*guard).finish(),
             Err(TryLockError::Poisoned(err)) => {
-                write!(f, "Mutex {{ data: Poisoned({:?}) }}", &**err.get_ref())
+                f.debug_struct("Mutex").field("data", &&**err.get_ref()).finish()
             },
-            Err(TryLockError::WouldBlock) => write!(f, "Mutex {{ <locked> }}")
+            Err(TryLockError::WouldBlock) => {
+                struct LockedPlaceholder;
+                impl fmt::Debug for LockedPlaceholder {
+                    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { f.write_str("<locked>") }
+                }
+
+                f.debug_struct("Mutex").field("data", &LockedPlaceholder).finish()
+            }
         }
     }
 }
diff --git a/src/libstd/sync/rwlock.rs b/src/libstd/sync/rwlock.rs
index 4757faabfb8..5c49d6b5845 100644
--- a/src/libstd/sync/rwlock.rs
+++ b/src/libstd/sync/rwlock.rs
@@ -428,11 +428,18 @@ unsafe impl<#[may_dangle] T: ?Sized> Drop for RwLock<T> {
 impl<T: ?Sized + fmt::Debug> fmt::Debug for RwLock<T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self.try_read() {
-            Ok(guard) => write!(f, "RwLock {{ data: {:?} }}", &*guard),
+            Ok(guard) => f.debug_struct("RwLock").field("data", &&*guard).finish(),
             Err(TryLockError::Poisoned(err)) => {
-                write!(f, "RwLock {{ data: Poisoned({:?}) }}", &**err.get_ref())
+                f.debug_struct("RwLock").field("data", &&**err.get_ref()).finish()
             },
-            Err(TryLockError::WouldBlock) => write!(f, "RwLock {{ <locked> }}")
+            Err(TryLockError::WouldBlock) => {
+                struct LockedPlaceholder;
+                impl fmt::Debug for LockedPlaceholder {
+                    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { f.write_str("<locked>") }
+                }
+
+                f.debug_struct("RwLock").field("data", &LockedPlaceholder).finish()
+            }
         }
     }
 }
diff --git a/src/libstd/sys_common/remutex.rs b/src/libstd/sys_common/remutex.rs
index 4d0407ccf6c..ce43ec6d9ab 100644
--- a/src/libstd/sys_common/remutex.rs
+++ b/src/libstd/sys_common/remutex.rs
@@ -116,11 +116,18 @@ impl<T> Drop for ReentrantMutex<T> {
 impl<T: fmt::Debug + 'static> fmt::Debug for ReentrantMutex<T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self.try_lock() {
-            Ok(guard) => write!(f, "ReentrantMutex {{ data: {:?} }}", &*guard),
+            Ok(guard) => f.debug_struct("ReentrantMutex").field("data", &*guard).finish(),
             Err(TryLockError::Poisoned(err)) => {
-                write!(f, "ReentrantMutex {{ data: Poisoned({:?}) }}", &**err.get_ref())
+                f.debug_struct("ReentrantMutex").field("data", &**err.get_ref()).finish()
             },
-            Err(TryLockError::WouldBlock) => write!(f, "ReentrantMutex {{ <locked> }}")
+            Err(TryLockError::WouldBlock) => {
+                struct LockedPlaceholder;
+                impl fmt::Debug for LockedPlaceholder {
+                    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { f.write_str("<locked>") }
+                }
+
+                f.debug_struct("ReentrantMutex").field("data", &LockedPlaceholder).finish()
+            }
         }
     }
 }
diff --git a/src/libsyntax_pos/lib.rs b/src/libsyntax_pos/lib.rs
index 2000db9703c..d30d79ece15 100644
--- a/src/libsyntax_pos/lib.rs
+++ b/src/libsyntax_pos/lib.rs
@@ -339,8 +339,11 @@ impl serialize::UseSpecializedDecodable for Span {
 }
 
 fn default_span_debug(span: Span, f: &mut fmt::Formatter) -> fmt::Result {
-    write!(f, "Span {{ lo: {:?}, hi: {:?}, ctxt: {:?} }}",
-           span.lo(), span.hi(), span.ctxt())
+    f.debug_struct("Span")
+        .field("lo", &span.lo())
+        .field("hi", &span.hi())
+        .field("ctxt", &span.ctxt())
+        .finish()
 }
 
 impl fmt::Debug for Span {